THE EFFECT OF POLYCYTHEMIA ON PLASMA VOLUME IN NEWBORN DOGS

Abstract

The effect of polycythemia(Hct 64-80) on plasma volume(PV) was studied in 27 unanesthetized, splenectomized puppies (age:6-14,post-spenectomy:5-13d). Normovolemic polycythemia(N) was induced in 9 pups by exchange transfusion(ExN) with 75cc/kg of red blood cells (RBC). Hypervolemic polycythemia(H) was induced in 11 pups by transfusion of 50cc/kg of RBC. 7 pups received ExT with 75cc/kg of whole blood and served as controls(C). PV(125I Fibrinogen) and red cell volume(RCV, by 51Cr) were measured prior to and 1,2, and 4hrs after transfusion, with the pups receiving no oral intake.Pups were fed 8cc/kg/hr after 4hrs, and measurements were repeated at 8 and 24hrs.RCV rose with transfusion in N and H and remained elevated throughout the experiment. RCV did not change in C. PV fell slightly in the C group prior to 4hrs and then rose to initial levels. PV rose in the N pups from -50±7%SD to -35±10%(p<.001),-37±8%,-38±9%, and after feeding to -29±13 and 1±18(p<.001),1,2,4,8 and 24hrs post-transfusion.PV fell in the H pups from 4±2% to -24±12(p<.001),-35±14, -37±14, and then rose after feeding to -32±9 and 0±15(p<.001). At 1,2,4 and 8hrs PV in H and N was different from that in C(p< .01).Thus pups with induced N or H equilibrate rapidly to a PV determined primarily by the Hct and not initial PV.Since the increase in PV in N prior to feeding was rapid and occurred during a period of no fluid ingestion, it must be due to a decrease in capillary pressure secondary to the induced change in viscosity. A further increase in PV to control levels occurs when the pups are fed, which is probably caused by renal solute retention.